Building with libzmq-dev from debian (so libzmq 2.x) results in the following error about an undefined symbol zmq_ctx_destroy:
make[3]: Leaving directory '/home/kanzure/local/bitcoin/bitcoin/src/secp256k1'
CXX zmq/libbitcoin_zmq_a-zmqabstractnotifier.o
CXX zmq/libbitcoin_zmq_a-zmqnotificationinterface.o
zmq/zmqnotificationinterface.cpp: In member function ‘void CZMQNotificationInterface::Shutdown()’:
zmq/zmqnotificationinterface.cpp:117:33: error: ‘zmq_ctx_destroy’ was not declared in this scope
zmq_ctx_destroy(pcontext);
^
Makefile:4328: recipe for target 'zmq/libbitcoin_zmq_a-zmqnotificationinterface.o' failed
make[2]: *** [zmq/libbitcoin_zmq_a-zmqnotificationinterface.o] Error 1
Switching to libzmq3-dev results in a successful build for me.
At doc/zmq.md there is text saying:
The ZeroMQ feature in Bitcoin Core uses only a very small part of the ZeroMQ C API, and is thus compatible with any version of ZeroMQ from 2.1 onward, including all versions in the 3.x and 4.x release series. Typically, it is packaged by distributions as something like libzmq-dev.
But see http://zeromq.org/intro:get-the-software which marks even libzmq 3.x as "legacy"; they follow semver and have major incompatibilities between major version field changes. Recent versions of libzmq should be compiled from source from here instead of APT repos.
Also, you can't have sockets from 2.x and 3.x talk to 4.x anyway.
